Treatment of the hair and skin with various creams or lotions with biologically active ingredients to improve hair growth and other conditions have generally low efficiency. A wide variety of externally applied agents are available for application to the hair to improve body, flexibility, curl, etc. These have limited and only shortterm term usefulness. Coloring hair with various dyes, that may be carcinogenic, requires frequent repetitions and is not always natural in appearance.
The use of biologically active compounds that are hair growth stimulators or that change other hair characteristics, such as color, would seem to be a more natural and attractive approach, especially at the stage where hair-follicle cells still exist but hair growth, for unknown reasons, is adversely affected. Attempts to follow this approach have been ineffective, possibly because of the inability of stimulators to penetrate the cellular membrane of hair follicle cells and to enter into the cells where their action is needed.
There is a need for improved methods of delivering compositions to hair follicles as a means of administering agents that affect hair growth, color and appearance. In general, the methods currently used for the topical delivery of biologically active substances to hair follicles are mainly based on diffusion of substances or their complexes with lipids. However diffusion of particles over large distances even for small particles is a very slow process. For example, the root mean square distance covered by particles like small molecules with a typical difflusion coefficient 5 10.sup.-6 cm.sup.2 s.sup.-1 for 1 day is only 1 cm. Accordingly, passive diffusion is not efficient for delivering particles of sizes 0.5.mu.m and larger to hair follicles.
Other methods that have been proposed for delivering agents to hair follicles, such as electroporation and the use of high pressure, results in the transdermal delivery of the substance to the systemic circulation are not specific for selective targeting of hair follicles. Accordingly, there is a present need for methods and apparatuses that selectively administer agents to hair follicles.